Nanocomposite materials exhibit many properties that are substantially different from those of the templated cores, such as different surface composition, magnetic properties, optical properties, high stability, and so on. As advanced composite functional materials with new properties, they have been found in extensive applications in many fields, such as microelectronics, communication, automobile, aerospace, defense, chemical, metallurgical, mechanical, biologic, pharmaceutical and optical industries. With the development of modern technology, the demands for materials having specialized properties are enhanced increasingly. Materials with only one component can hardly meet these requirements, while nanocomposite particles with core-shell structure have the feature of designability. Advanced composite particles with new properties can be created by utilizing multi-composite and nonlinear composite effects.
As one of important inorganic fillers, calcium carbonate is widely used in many fields, such as rubber, plastic, paint, printing ink, coating, paper, toothpaste and cosmetic and the like. Owing to its surface hydrophilia and oleophobic properties, calcium carbonate has a poor affinity with organic high polymer and bad dispersion in high polymer, which causes defects in the interface of two materials, thereby decreasing mechanical properties of composite materials. In order to improve its application performance, calcium carbonate needs surface modification. Previously, surface modifications for calcium carbonate focus on organic modifications, which are classified into two types: (1) Treatment with surfactants. The surface of calcium carbonate is treated with anionic, cationic and nonionic surfactants, such as fatty acids, esters, alcohols and acidamides. These substances tend to form a coating layer on the surface of calcium carbonate to make it compatible with polymers, and thereby improving the mechanical behaviors of the materials. (2) Treatment with coupling agents. At present, the surface modification for calcium carbonate with coupling agents is a fastest-developed modification technique. There are usually several kinds of groups with different properties and functions in coupling agent molecules. Some of them can react with various groups on the surfaces of the fillers to form chemical bonds, while others can physically wrap around the surface or react with polymer macromolecules. Coupling agents in themselves should have longer flexible hydrocarbon chains, which favor to enhance the stress at the interface layer and to improve the ability of the interface layer to absorb or scatter impact energy, and thereby enhancing over-all properties of materials. There are various kinds of coupling agents, such as silicon, titanium, aluminum, chromium, zirconium, and zinc series.
Silica (SiO2.nH2O) is a good reinforcing white filler for rubber. There are two reasons as follows: (1) there are large quantities of silanol groups having affinity with rubber, plastic and fiber on the surfaces of silica particles, which can cause polymers to form linkage with SiO2.nH2O particles; and (2) SiO2.nH2O particles have large surface areas and abundant chain structures. Industrial superfine calcium carbonate with best quality has a BET surface area ≧26 m2/g. Therefore, polymers have larger contact area with silica particles than with calcium carbonate, which benefits to form linkage at the interface of two materials, thereby improving mechanical properties of materials. However, it is very necessary to develop the inexpensive products to partly or completely replace silica due to the higher price of SiO2.nH2O.
Hua et al. had microcrystal analysis XRD and XPS studies for SiO2-coated CaCO3 superfine particles, indicating that the SiO2-coated superfine CaCO3 has a particle size of about 130 nm. See Hua Y. M. et al, Chin. J. Inorg. Chem., 2001, 17(1): 135-138. However, the particle size doesn't meet the requirement of nanomaterials. Furthermore, there is no report on composite particles of calcium carbonate coated by other components.
Owing to their large BET surface areas and absorbing capacity, inorganic porous materials have been widely used as catalysts and absorption materials. According to different pore sizes, porous materials can be classified into microporous materials, mesoporous materials, or macroporous materials. In general, microporous materials have pore diameters of 2 nm or less, mesoporous materials have pore diameters of 2 to 50 nm, and macroporous materials have pore diameters of 50 nm or more. However, mesoporous materials have the disadvantages of irregular pores and wide-distribution dimensions. See Beck J. S. et al, J. Am. Chem. Soc. 1992, 114: 10834-10843. In addition, the preparation method for mesoporous materials usually involves a complicated procedure and a high cost, while a method with low cost and facile process is preferred.
Therefore, one object of the present invention is to provide composite materials of CaCO3 and SiO2.nH2O.
Another object of the present invention is to provide SiO2.nH2O materials with hollow structures.
A further object of the present invention is to provide SiO2.nH2O mesoporous nanomaterials with hollow structures.
A still further object of the present invention is to provide a preparation method for the above-mentioned composite materials and mesoporous materials.